U.S. Pat. No. 6,436,843 B1 discloses a method for applying a coating material on a substrate, wherein a print head is disposed over a substrate which is supported by a chuck. A digital signal processor provides control signals for controlling process parameters for dispensing drops of coating material and for controlling the relative position of the print head and the chuck. The manner in which the relative position between the print head and the chuck is determined is not disclosed.
US2007/169806 A1 discloses a print assembly including a print head and a camera having high magnification capabilities mounted in a rigid mount. The rigid mount with the print head and the camera are mounted over a conveyor for supporting wafers. A computer/workstation is coupled to receive and process imaging data from the camera. With this setup the rigid mount carrying the print head and the camera can be calibrated and registered with respect to a wafer which is on the conveyor. The camera having high magnification capabilities is relatively expensive.
WO2011/026880 A1 discloses a system and a method for centering a print track, on a substrate. Firstly, a printing station deposits a first print track and a marker element. Secondly, a second print track is deposited in a second step, which second print track includes a centering interruption which is positioned and centered with respect to the marker element. The known method, which is primarily concerned with aligning subsequently applied screen printing patterns, may include use of an inspection system including a CCD camera. The inspection system may locate the position of certain features of an incoming substrate and may communicate the inspection results to a system controller for analysis of the orientation and position of the substrate to assist in the precise position of the substrate under a printing head prior to processing the substrate.
U.S. Pat. No. 7,611,217 B2 discloses a method and a system for inkjet drop positioning. The known method includes determining an intended deposition location of an ink drop on a substrate. To that end an ink drop is deposited on the substrate using an inkjet printing system. Subsequently, a deposited location of the deposited ink drop on the substrate is located and the deposited location is compared to the intended location. Then, the difference between the deposited location and the intended location is determined and the difference between the deposited location and the intended location is compensated by adjusting a control parameter of the inkjet system.
This method is time consuming because it has to be done for each wafer that has to be processed. In view thereof, the known system is not suited for a high volume inkjet printer system.
EP 1 888 336 discloses an inkjet printing system including a calibration camera and a vision camera assembly and a feducial mark on the calibration camera assembly. The vision camera assembly includes a high resolution camera and a low resolution camera with a greater field than the high resolution camera, typically in the order of 10 mm by 10 mm. With the calibration camera the position errors between the print heads can be determined by looking at the printing heads with the calibration camera. When errors are found, these may be adjusted. Both the vision camera assembly and the calibration camera assembly are able to look at the feducial mark in order to coordinate vision camera assembly and the calibration camera assembly. Once relative positioning between calibration camera assembly and machine vision camera assembly is known, relative positioning between print heads, calibration camera assembly, and machine vision camera assembly may be determined by a computer and may be used for print head and print head carriage adjustment. Further, relative positioning between vision camera assembly and print head carriage frame may be known through the use of common optical strip. This may generally allow a computer to determine relative positioning between substrate and print heads and determine any positioning error therebetween.
In order to accurately determine the position of a wafer relative to a printing head, an expensive dual camera vision assembly including a high resolution and a low resolution camera is necessary as well as a calibration camera assembly. The accuracy and the precision of the known measurement system is determined by the accuracy of the positions of the various cameras. In view thereof, the carriages of the various cameras must be very robust in order to ensure that the relative positions of the cameras of the two systems remain intact. Such robust movable camera carriages are expensive.